Photographic observations of meteors carried out in Dushanbe by the method of instantaneous exposure have shown clearly that meteoroids entering the Earth's atmosphere are subjected to different types of fragmentation. The quasi-continuous fragmentation of meteoroids is mostly widespread. Using the physical theory of meteors which takes into account the quasi-continuous fragmentation of meteoroids and on the basis of light curves of meteors the densities of meteoroids of different streams have been determined. The results enable us to conclude that the densities of meteoroids are over an order of magnitude higher than they have been assumed before. Moreover they are close to the densities of carbonaceous and ordinary chondrites.